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TECHNICAL REPORTS
Energy Saving Technologies for Elevators
Authors: Junichiro Ishikawa*, Hirokazu Banno* and Sakurako Yamashita*
1. Introduction
In recent years, interest in energy saving has been
increasing both in Japan and overseas, as well as in
creating a low-carbon society. In the building industry
too, there are moves to standardize methods for evaluating energy saving performance, mandate the reporting of energy saving performance, and also require the
installation of facilities for improving energy saving
performance. Amid this changing environment, there is
growing competition to develop new devices and technologies in many fields related to energy saving.
In the manufacture and development of elevators,
energy saving performance has always been important,
and new models have offered improved performance.
Because the energy consumed by an elevator varies
greatly according to its specifications and type of use, it
is difficult to evaluate performance using a standard
pattern.
This paper summarizes the trends in energy saving
technology for elevators and the power consumption
characteristics of elevators that use this technology. It
also describes the energy saving technology used in the
standard “AXIEZ” elevator, which underwent a model
change in June 2011, together with its effectiveness.
2. Transition of Energy Saving Technology
The following table 1 shows the transition of drive
control methods used in traction elevators and the
energy consumed by them.
Regarding high-speed elevators that travel at 120
m per minute or faster, in the latter half of the 1970s,
the MG set was changed to the thyristor Leonard
method, and the control circuit was replaced by a microprocessor. As a result of this switch to electronics,
the control performance was greatly improved, and an
energy saving of about 40% was attained.
For a low-speed elevator that travels at no more
than 105 m per minute, an induction motor fitted with a
reduction gear was used. This type of elevator was
widely used as the standard type of elevator in mediumto low-rise buildings. During the early 1970s, a thyristor
was used to control the primary voltage applied to the
induction motor, which enabled the speed of the elevator to be controlled more or less continuously. As a
result, riding comfort was significantly improved, and
the motor efficiency during acceleration and deceleration was increased. These improvements, together with
the incorporation of a microprocessor in the control
circuit, resulted in a 20% increase in efficiency compared to the conventional model.
Subsequently, power transistors with excellent
control characteristics appeared on the market, and
great progress was made in the technology for a variable voltage variable frequency (VVVF) control method
using these transistors, in other words, an inverter
control method.
Table 1 Transition of drive control method and energy consumption
High-speed elevator
Model
Decade
Ward-Leonard
Control circuit
Relay circuit
Hoisting General
device
Ultra(motor)
high-
Energy
consumption
Gearless (DC motor)
AC 2-step
speed control
2010
2000
VVVF (inverter)
Microprocessor
Gearless (DC motor)
100%
1990
Thyristor
Leonard
speed
Control circuit
Low-speed elevator
1980
Motor control
method
Motor control
method
95 72
%%
Helical gear type
(induction motor)
Slim-type centrally
wound construction
Gearless
Gearless
(induction motor)
62%
(permanent magnet-type
synchronous motor)
57%
Primary voltage
control
54%
52%
VVVF (inverter)
Relay circuit
Microprocessor
Gearless
Hoisting device
(motor)
Worm gear type (induction motor)
Machine room
Machine room exists
Energy
consumption
*Inazawa Works
1970
Helical gear Gearless
(permanent magnet-type
(permanent
synchronous motor)
type
magnet-type
Slim-type centrally wound
synchro(induction motor) nous
motor)
construction
100%
93% 74%
37%
Machine room does not exist
32%
30%
29%
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TECHNICAL REPORTS
3. Component Devices of an Elevator, and
Energy Consumption
Figure 1 shows the construction of an elevator.
Figure 2 shows power waveform of a hoisting device
motor.
Among the various devices, the one that consumes
the greatest amount of power instantaneously is the
hoisting motor which raises and lowers the weight that
balances against the weight of the car. Next is the electromagnetic brake that prevents the hoisting device from
rotating, followed by the door motor that opens and closes
the car doors. Because these devices are used only while
the elevator is moving, they do not consume much energy
Speed regulator
Machine room
Hoisting device
Control panel
Rope
Upper car station
Door motor
Car
Car door
Balance weight
Entrance button
Entrance door
Entrance
Hoistway
Rotational speed (%)
Fig. 1 Construction of an elevator
Ascending
Descending
Time
Power consumption (%)
Mitsubishi was the first company in the world to
develop an elevator inverter, and in 1983, succeeded in
making a commercially viable high-speed elevator.
Inverter control is not only efficient, but also has characteristics which improve the power factor of the power
source. As a result, it was possible to increase the
efficiency by around 10% and also reduce the capacity
of the power source facilities in the building by about
20%. In addition, the excellent control performance of
this system permitted fine control of even induction motors, thus ensuring excellent riding comfort and highly
efficient acceleration and deceleration. Particularly, in the
case of a low-speed elevator, it was possible to increase
the efficiency by a dramatic 50% compared to the conventional primary voltage control method.
In 1990, a helical gear-type hoisting device was
commercialized to replace the existing less-efficient
worm gear hoisting device, thus improving transmission
efficiency and riding comfort.
Around the mid 1990s, a gearless hoisting device
incorporating a permanent magnet synchronous motor
(hereafter called a “PM gearless hoisting device”) was
commercialized for high-speed (at least 120 m/min) and
ultra-high-speed (at least 300 m/min) elevators. The use
of permanent magnets led to a multi-polar compact motor,
which was more efficient than an induction motor.
In 1998, Mitsubishi released an elevator that does
not require a machine room. In order to house the
hoisting device and the control panel for this elevator
inside the hoistway, a very quiet PM gearless hoisting
device was adopted for low-speed elevators. To make
the control panel slimmer, the drive section and power
supply section were closely integrated. Also, a switching power supply was used as the control power supply
to ensure a stable power supply voltage and reduce the
conversion loss, thus reducing the power consumption.
In 2001, Mitsubishi developed a slim-type PM
gearless hoisting device which required even less
space and allowed flexibility of layout, resulting in the
rapid spread of machine room-less elevators. The
motor diameter was increased, its thickness reduced,
and a centralized winding construction was employed,
significantly reducing copper loss and thus saving
energy. At present, the PM gearless hoisting device is
the main kind of hoisting device used throughout the
entire range from ultra-high speed to high speed. Along
with the increasing demand for energy saving, slim
hoisting devices using a centralized winding construction are employed for high-speed elevators as well,
resulting in energy saving.
In this way, advances in motor drive technology
over the past several decades have led to good riding
comfort and space saving in elevators, and have also
saved energy.
Power
running
100% load
50% load
0% load
0% load
50% load
100% load
Regeneration
Time
Fig. 2 Power waveform of a hoisting device motor
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TECHNICAL REPORTS
Energy consumption
Percentage of energy consumed (%)
Total energy consumption
Percentage occupied by
control devices
Percentage occupied by
lighting
Percentage occupied by
the hoisting device motor
* The elevator starting intervals are equal
for each starting frequency.
Low
Starting frequency
High
Fig. 3 Relationship between the starting frequency of an elevator and the energy consumed
while the elevator is moving short distances.
Figure 3 shows the relationship between the starting
frequency of an elevator and the energy consumed by
the devices. Many low-speed elevators are used at low
starting frequency. Under this condition, the absolute
power consumption is small, but the percentage of the
total electrical energy that is consumed continuously by
the control devices is large. The lighting remains lit while
the elevator is moving and also for a fixed period after it
has stopped, so it is lit continuously when the starting
frequency is low. Consequently, in the region where the
starting frequency is low, the percentage of the total
energy consumption is large. The percentage in the case
of a hoisting device motor is high in the region where the
starting frequency is high.
As shown, the device that affects the total energy
consumption changes according to the starting frequency. In addition, apart from the starting frequency,
the energy consumption also changes according to the
specifications of the devices and the car occupancy.
These conditions differ greatly from one building to
another, and change over time, so it is difficult to evaluate the energy saving performance of elevators in
different buildings by using a specific representative
pattern. Also, in order to effectively reduce the energy
consumption under a variety of conditions, it is necessary to combine multiple methods according to each
starting frequency.
Conventionally, incandescent lamps or fluorescent
lamps have been used to illuminate the elevator car, but
the life of such lighting appliances depends greatly
upon the number of times that they are switched on.
For this reason, the lighting is kept on for a fixed period
after the elevator stops, thus reducing the number of
times that it can be switched on and extending its life.
But with this method, the lighting is actually on for
longer than necessary, so there is a limit to the energy
saving effect of the automatic switch-off function. Recently, LED light sources have become cheaper and
increasingly popular. One of their main features is that
their life is determined mainly by the time during which
they are on rather than by the number of times that they
are switched on.
All standard “AXIEZ” elevators use LED lighting in
the ceiling of the car as the main kind of lighting. As a
result, the electric power consumed by the LED ceiling
lights is about half of that consumed by conventional
fluorescent ceiling lights, and about 1/8 of that consumed by incandescent lights. Also, by reducing the
time delay until the lamps are automatically turned off,
the necessary standby power is reduced. In addition, the
life of an LED light is about 3.3 times that of a fluorescent
light, and about 26 times that of an incandescent light,
thus reducing the lamp replacement frequency.
By increasing the life of the lighting appliances and
reducing the energy consumed by them, the life cycle
cost and environmental impact are reduced.
4. “AXIEZ” Energy Saving Technology
4.2 Technology for utilizing energy regeneration
4.1 LED lighting
As mentioned above, the power consumed by the
lighting of an elevator car is reduced by a function that
automatically switches off the lighting after the elevator
car stops. Consequently, the lighting in an elevator car
is switched on much more frequently than general
lighting.
4.2.1 Regenerative converter system
An elevator is suspended by a cable to which a
weight is attached that balances against the weight of
the car. By driving this cable with a motor, the elevator
moves up or down. The balance weight is balanced
against the car when the car is occupied by about half
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TECHNICAL REPORTS
of the rated number of passengers. If this weight balance is upset, the motor will be pulled to the heavier
side. As a result, when the heavier side is raised, potential energy will be accumulated. Conversely, if the
balance weight moves to the side that is pulled, the
motor can be used as an electric generator, and the
potential energy can be recovered as regenerative
energy. In this way, the elevator is designed to capture
a large amount of regenerative energy from potential
energy in addition to kinetic energy.
High-speed elevators have always made effective
use of regenerative energy by using a regenerative
converter.
As shown in Fig. 4, the electrical circuit of the elevator is designed such that regenerative power returned
from the motor is connected directly to the power
source system of the building via a regenerative converter. This enables the regenerative power to be reused efficiently.
Most low-speed elevators are installed in small
buildings, so it is usually not possible to acquire facilities that can adequately consume regenerative electric
power, and also there are size and cost limitations, so
generally, the regenerative electric power is consumed
by a resistor. However, in a medium- to large-scale
building, there is currently no solution to this problem,
even if there are adequate facilities. To overcome this
issue, the regenerative converter of the “AXIEZ” elevator, which does not have a machine room, has been
made sufficiently small that it can be installed in the
hoistway. It is hoped that in the future, this technology
will help save energy in low-speed elevators.
4.2.2 Regenerative electric power storage system
As mentioned above, a regenerative converter often cannot be used in a small building. The ELE SAVE,
Converter
which Mitsubishi released in 2001, incorporates a
nickel-hydrogen battery which provides enough power
to operate the elevator for 10 minutes in the event of a
power outage. The battery stores the regenerative
electric power, and reuses it while the elevator is running, thus realizing an energy saving of about 20%.
This system enables regenerative electric power to be
used in small buildings as well.
As a result of recent competition to develop electrical storage devices for power applications, the energy
density, output density, repeated charging/discharging
durability, and charging/discharging efficiency have
improved. Among these storage devices, an electrical
2-layer capacitor has excellent repeated charging/discharge durability and high charging/discharging
efficiency, and is environment-friendly. The ELE
CHARGE regenerative storage system which Mitsubishi
has commercialized uses an electrical 2-layer capacitor
as the storage device. Although such a capacitor has
the abovementioned merits, in order to incorporate it
into an elevator, it was necessary to take countermeasures against deterioration caused by energizing the
capacitor at high temperature, and also to design a
circuit configuration and control method that made the
most of the merits of the capacitor. To resolve these
issues, the circuit of the ELE CHARGE was optimized
and technology for monitoring the capacitor temperature and voltage was newly developed, thus at least
doubling the replacement interval compared with a
secondary battery, and also achieving an energy saving
effect of about 25% (Fig. 5).
4.3 Energy saving effect
A simulation evaluation of the energy consumed by
the energy saving technologies mentioned so far was
carried out. The results are shown in Tables 2 and 3.
Capacitor
Inverter
PM
Velocity feedback
Inverter
control circuit
Car
Rotor angle feedback
Converter
control circuit
Gate drive
circuit
Current feedback
Phase
detection
circuit
Gate drive
circuit
Voltage feedback
3-phase AC power supply
Current detector
Permanent magnet motor
Encoder
Balance
weight
Line filter
Current feedback
PS:
CT:
PM:
RE:
RE
CT
AC reactor CT
PS
Controller
Fig. 4 Drive system for an elevator with a regenerative converter
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TECHNICAL REPORTS
Converter
Inverter
Capacitor
RE
CT
Line filter
PM
3-phase AC power supply
Current detector
Permanent magnet motor
Encoder
Gate drive
circuit
Converter
control circuit
Inverter control
circuit
Car
Velocity feedback
PS:
CT:
PM:
RE:
Converter
Rotor angle feedback
Electrical 2-layer
capacitor
Current feedback
Balance
weight
PS
Controller
Fig. 5 Regenerative electric power storage system
The simulation was carried out under the operation
conditions in chronological order, based on the measurement data of the traffic pattern.
Table 2 shows the energy consumption improvement of the “AXIEZ” compared to the conventional
model. By adopting energy saving technologies such as
LED lighting, the energy consumption can be reduced
by up to 20% compared to that of the conventional
model. Also, by using LEDs for lighting, which accounts
for a large proportion of the energy consumed, automatic switching-off of the lights can be optimized. Particularly, in a building where the operation frequency is
low, a large energy saving effect will be obtained.
Table 3 shows the energy consumption improvement which depends upon whether or not the regenerative converter system and/or the regenerative power
storage system are used. Compared to when the regenerative converter system is not used, the energy
consumption is reduced by up to 35%, and also compared to when the regenerative power storage system
is not used, the energy consumption is reduced by up
to 25%. Also, with both systems, the improvement of
energy consumption tends to increase as the number of
passengers and also the operation frequency increase.
As mentioned above, the “AXIEZ” delivers excellent energy saving performance over a wide range of
specifications and applications due to the use of LED
lighting and technology for utilizing regeneration.
5. Conclusion
This paper summarized the transition of energy
saving technology for elevators and the power consumption characteristics of elevators that use this
technology. It also described the new technology used
in the new “AXIEZ,” and its effectiveness.
Table 2 Improvement of energy consumption of AXIEZ
Application
Floor
Residence:
9-person elevator
5th floor
9th floor
5th floor
10th floor
5th floor
10th floor
Office: 11-person
elevator
Office: 15-person
elevator
Energy consumption
improvement
20%
18%
17%
13%
13%
11%
Table 3 Improvement of energy consumption due to
technology for utilizing regeneration
Application
Floor
Residence: 5th floor
9-person
9th floor
elevator
Office:
5th floor
11-person
10th floor
elevator
Office:
5th floor
15-person
10th floor
elevator
Regenerative Regenerative electric
converter system power storage system
improvement
improvement
5%
2%
14%
10%
19%
12%
30%
21%
30%
25%
35%
20%
In the future, the authors will work on promoting
technologies for utilizing regeneration, and also reducing additional energy consumption caused by each
device, in order to help prevent global warming.
6. Reference
IKEJIMA Hiroyuki, ARAKI Hiroshi, SUGA Ikuro, TOMINAGA Shinji: Mitsubishi Energy Saving-type ELE SAVE
Automatic Backup Device for Operating an Elevator in
the Event of a Power Failure, Mitsubishi Giho, 75, No.
12, 782−785 (2001)
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